* {
  margin: 0;
  padding: 0;
}
@media screen and (min-width: 320px) {
  html {
    font-size: 21.33PX;
  }
}
@media screen and (min-width: 720px) {
  html {
    font-size: 50PX;
  }
}
div {
  width: 2rem;
  height: 2rem;
  background: blue;
}
